US4984546A

US4984546A - Engine control apparatus

Info

Publication number: US4984546A
Application number: US07/363,661
Authority: US
Inventors: Setsuhiro Shimomura; Seiji Wataya; Yukinobu Nishimura; Satoru Okubo
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1988-06-08
Filing date: 1989-06-08
Publication date: 1991-01-15
Anticipated expiration: 2009-06-08
Also published as: DE3918772A1; DE3918772C2; KR900000578A; KR930000007B1; US5058552A

Abstract

An engine control apparatus is provided with a control unit in which a fuel supply quantity Q_f or a ignition timing θ_i is corrected to maximize an evaluation parameter A=P_i /(Q_a /N) obtained on the basis of a suction air quantity Q_a, an engine speed N and a mean effective pressure P_i in a engine, or to maximize a parameter B=P_i /P_b obtained on the basis of a suction pipe pressure P_b and the mean effective pressure P_i, or to maximize a maximum pressure P_max or a mean effective pressure P_i for every combustion cycle, so that control is performed on the basis of the result of the above correction. The control unit also performs the feedback control of the fuel supply quantity Q_f and corrects the ignition timing by the above-mentioned correction means. Further, the control unit performs feedback control in a predetermined load-operation range of the engine, and stops the feedback control and corrects the fuel supply quantity Q_f out of said predetermined load-operation range of the engine.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine control apparatus in which maximum power and maximum efficiency can be obtained in spite of scatter in performance of engines.

2. Prior Art

Heretofore, there has been used an apparatus for controlling a fuel injection valve and an ignition device by calculating a proper fuel supply quantity and ignition timing on the basis of the relationship between a suction air quantity or suction pipe pressure and an engine speed (rpm).

Further, a control apparatus designed to perform higher-precision control by detecting the combustion pressure of the engine and adjusting the pressure to a predetermined value has been disclosed in Japanese Pat. Unexamination Publication No. 62-85148.

In this control apparatus, the combustion condition is detected by the output of a cylinder internal pressure (combustion pressure) sensor provided in every cylinder so that the controlling of combustion injection timing, EGR (exhaust gas recycle) valves and the like are carried out to fit the condition in a predetermined pattern.

In the aforementioned prior art apparatus, control is carried out to fit the combustion pressure to a combustion pattern determined in advance by a standard engine. In the case where a large number of engines are mass-produced, there arises considerable scatter. Accordingly, individual engines require individually different combustion patterns. For this reason, it cannot be absolutely said that precision in controlling is improved by controlling the combustion pressure by use of a uniform standard pattern. On the contrary, the performance of the engine may be rather lowered by such control.

Further, in the prior art apparatus, the fuel injection timing, the EGR rate and the like are controlled as operation parameters for controlling the combustion pressure. However, the most effective parameters for the output performance of the engine are the combustion injection quantity and ignition timing optimum thereto.

In general, the freely controllable range of the fuel injection quantity is limited for the purpose of suppressing the component concentration of the exhaust gas to a low level. Accordingly, it is necessary to control the fuel injection quantity and the ignition timing comprehensively to reconcile the components of the exhaust gas and the power performance of the engine.

Further, in a gasoline engine, in order to clean up exhaust gas and improve the output power of the engine, it is necessary to properly control the air-fuel ratio and ignition timing in accordance with the operating condition of the engine. Therefore, a method using a micro-computer to control the air-fuel ratio and ignition timing has been widely used in the field of car gasoline engine.

For example, the air-fuel ratio control based on the quantity of fuel injection is carried out in such a manner as follows. The quantity of suction air (Q_a) in the engine is detected by an air-flow sensor provided in an air-intake passage. The engine speed or the number of engine revolutions per unit time (N_e) is obtained from the output of a rotation sensor provided on a crankshaft or the like. The quantity of air per engine revolution (Q_a /N_e) is calculated and, accordingly, the quantity of basic fuel injection is calculated based on the quantity of air (Q_a /N_e). The quantity of basic fuel injection is used for the purpose of obtaining a target air-fuel ratio at every predetermined operation point. Then, a correction is carried out in accordance with the output of a water sensor or the like provided to detect the temperature of engine cooling water to thereby finally decide the quantity of fuel injection. On the basis of an injection pulse signal having a pulse width corresponding to the thus decided fuel injection quantity, an injector is actuated to open its valve in synchronism with the rotation of the engine to inject fuel into, the engine. Further, in a low and partial load range, an air-fuel ratio sensor in which the output thereof rapidly changes in the vicinity of the theoretical air-fuel ratio is used to thereby judge whether the actual air-fuel ratio is on a rich side or on a lean side. A feedback correction based on the judgment is applied to the quantity of fuel injection so that the air-fuel ratio of the engine is controlled so as to be converged into the theoretical air-fuel ratio. By controlling the air-fuel ratio to be always the theoretical air-fuel ratio, cleaning of exhaust gas can be carried out with high efficiency by used of ternary catalystic method.

On the other hand, the control of ignition timing is carried out in such a manner as follows. In general, an ignition timing advance predetermined in the form of a map corresponding to the air quantity (Q_a /N_e) and the engine speed (N_e) is read. The current conduction of an ignition coil is controlled by an ignition signal based on the thus read-out ignition timing advance.

In general, the ignition timing advance is determined so as to aim at MBT (minimum ignition timing advance required for producing maximum engine torque). Because MBT varies widely according to several factors, such as scatter in engine temperature and air-fuel ration, dimensional error in the combustion chamber, temperature and humidity of suction air and the like, it is difficult to obtain optimum ignition timing continuously by such a simple "open" control method. There exists a problem in that knocking trouble may occur or reduction of torque may occur. Therefore, such an improvement has been proposed as described in Japanese Pat. Unexamination Publication No. 62-82273. The improvement is constructed so that the ignition timing feedback control is carried out on the basis of the measured value of cylinder internal pressure to maximize the engine torque. According to the cylinder internal pressure feedback control method, for example, a rotation sensor is provided to generate a pulse for every degree (1° C.) of crank angle. The output value (P₀) of the cylinder internal pressure sensor measured for every pulse generation is read successively, so that mean effective pressure (P₁ ) represented by the following equation is calculated from cylinder volume (V) and piston displacement (V_n) corresponding to the currently obtained crank angle. ##EQU1## Consequently, the ignition timing feedback control is carried out to maximize P₁.

As described above, the conventional cylinder internal pressure feedback controlling method has an attempt to obtain maximum torque by correcting ignition timing to maximize mean effective pressure (P₁). However, the air-fuel ratio feedback control is stopped in a high load range, so that "open" control is carried out in the high load range. Accordingly, air-fuel ratio error caused by scatter in characteristics of sensors, injectors and fuels is produced as reduction of torque. Accordingly, it is impossible to draw out the best in the torque of the engine even if cylinder internal pressure feedback control is carried out by correcting ignition timing.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an engine control apparatus which is capable of controlling the combustion condition of an engine suitably corresponding to the operation condition of the engine and capable of drawing out maximum power and maximum efficiency to thereby solve the aforementioned problem.

It is another object of the present invention to provide an engine control apparatus which is capable of drawing out the best in the torque of the engine even in a high load range by a cylinder internal pressure feedback control method to thereby solve the aforementioned problem.

The engine control apparatus according to the present invention is provided with a control unit in which the fuel supply quantity Q_f or the ignition timing θ_i is corrected so as to maximize the evaluation parameter A=P_i /(Q_a /N) obtained on the basis of the suction air quantity Q_a, the engine speed N and the mean effective pressure P_i in the engine, or to maximize the parameter B=P_i /P_b obtained on the basis of the suction pipe pressure P_b and the mean effective pressure P_i, or to maximize the maximum pressure P_max or mean effective pressure at P_i at every combustion cycle, so that control is performed on the basis of the result of the above correction.

Also, the internal combustion engine control apparatus according to the invention is provided with a control unit which performs the feedback control of the fuel supply quantity Q_f and corrects the ignition timing by the above-mentioned correction means.

Further, the internal combustion engine control apparatus according to the invention is provided with a control unit which performs feedback control in a predetermined load-operation range of the engine, and stops the feedback control and corrects the fuel supply quantity Q_f in other operation ranges of the engine.

Further, the engine control apparatus according to the present invention comprises: an air-fuel ratio control means for controlling the air-fuel ratio of an engine; an ignition timing control means for controlling the ignition timing of the engine; an air-fuel ratio detection means for detecting the air-fuel ratio of the engine; a load detection means for detecting the load of the engine; a cylinder internal pressure detection means for detecting the internal pressure of a cylinder of the engine; a first cylinder internal pressure feedback control signal generation means responsive to the output of the cylinder internal pressure detection means for generating a first cylinder internal pressure feedback control signal and for applying the first cylinder internal pressure feedback control signal to the ignition timing control means to thereby substantially maximize the output torque of the engine on the basis of the cylinder internal pressure; a load judgment means responsive to the output of the load detection means for judging whether the load of the engine is in a low or partial load range or in a high load range; an air-fuel ratio feedback control signal generation means for generating an air fuel ratio feedback control signal and for applying the air-fuel ratio feedback control signal to the air-fuel ratio control means to thereby converge the air-fuel ratio to a theoretical value when the load judgment means proves that the load of the engine is in the low or partial load range; and a second cylinder internal pressure feedback control signal generation means for generating a second cylinder internal pressure feedback control signal and for applying the second cylinder internal pressure feedback control signal to the air-fuel ratio control means to thereby substantially maximize the torque of the engine when the load judgment means proves that the load of the engine is in the high load range. The apparatus has a feature particularly in that the air-fuel ratio feedback control as well as the ignition timing feedback control is carried out to substantially maximize the torque of the engine in a high load range in which the air-fuel ratio feedback control has not been carried out in the prior art.

The control apparatus according to the present invention obtains the maximum pressure P_max or the mean effective pressure P_i for every combustion cycle on the basis of the combustion chamber pressure P_c and the crank angle θ_c, corrects the fuel supply quantity Q_f or the ignition timing θ_i to maximize at least one of the maximum pressure P_max, the mean effective pressure P_i and the evaluation parameters A and B, and supplies fuel to the engine on the basis of the corrected fuel supply quantity Q_f or performs ignition control based on the corrected ignition timing θ_i.

Also, the control apparatus according to the invention detects the air-fuel ratio based on the component concentration of a combustion gas detected by the exhaust sensor, performs the feedback control of the fuel supply quantity Q_f to make the air-fuel ratio be a predetermined value, and corrects the ignition timing θ_i to maximize at least one of the maximum pressure P_max, the mean effective pressure P_i and the evaluation parameters A and B.

Further, the control apparatus according to the invention detects the air fuel ratio based on the component concentration of a combustion gas detected by the exhaust sensor, perform the feedback control of the fuel supply quantity Q_f to make the air-fuel ratio be a predetermined value, and stops the feedback control in a predetermined load-operation range of the engine and, at the same time, corrects the fuel supply quantity Q_f to maximize at least one of the maximum pressure P_max, the mean effective pressure P_i and the evaluation parameters A and B.

Further, in a low or partial load range, the air-fuel ratio feedback control means is operated to carry out the air fuel ratio feedback control based on the output of the air-fuel ratio detection means. As this result, the air-fuel ratio of the engine is substantially converged into a theoretical air-fuel ratio. Further, the ignition timing feedback control is carried out based on the output of the cylinder internal pressure detection means to substantially maximize the torque of the engine.

In a high load range, both the ignition timing feedback control and the air-fuel ratio feedback control are carried out based on the output of the cylinder internal pressure detection means. As a result, the internal pressure (combustion pressure) of the cylinder is controlled so that maximum torque can be obtained under the condition that the air-fuel ratio is rich.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the internal combustion engine control apparatus as one embodiment of the present invention;

FIG. 2 is a block diagram showing the internal construction of the control unit in the embodiment of FIG. 1;

FIG. 3 is a characteristic graph showing an example of the combustion pressure waveform in the embodiment of FIG. 1;

FIGS. 4 and 5 are characteristic graphs showing the relationships between the combustion parameters, the air-fuel ratio and the ignition timing, respectively;

FIGS. 6(a) through 6(c), 7 and 8 are flow charts showing the flow of the operation for performing the maximum value control according to the present invention, respectively;

FIG. 9 is an explanatory view showing an example of the zone separation of the operation condition and the assignment of the memories;

FIG. 10 is a flow chart showing the flow of the operation in a transient state according to the present invention;

FIG. 11 is a diagram showing the whole configuration of the engine control apparatus according to another embodiment of the present invention;

FIG. 12 is a partly block diagram showing the embodiment;

FIGS. 13 through 15 are characteristic graphs for explaining the controlling operation of the embodiment, respectively; and

FIG. 16 is a flow chart for execution of the controlling operation of the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the main construction of an embodiment of the present invention. In the drawing the reference numeral 1 designates an air cleaner; 2, an air-flow meter for measuring the quantity of suction air; 3, a throttle valve; 4, a suction air manifold; 5, a cylinder block; 6, a water temperature sensor for detecting the temperature of engine cooling water; and 7, a crank angle sensor.

The crank angle sensor 7 generates a reference position pulse at every reference position of the crank angle (for example, for every 180 degrees in a 4-cylinder engine or for every 120 degrees in a 6-cylinder engine) and generates a unit angle pulse for every unit angle (for example, for every 1 degree).

The reference numeral 8 designates an exhaust manifold; 9, an exhaust sensor for detecting the component concentration (for example, oxygen concentration) of an exhaust gas; 10, a fuel injection valve; 11, an ignition plug, 13 a cylinder internal pressure sensor (hereinafter referred to as "combustion pressure sensor") for detecting the internal pressure of the cylinder; and 15, a control unit.

In the control unit 15, the instantaneous crank angle can be known by counting the number of unit angle pulses after the input of a reference position pulse.

Further, the engine speed can be known by measuring the frequency or cycle of the unit angle pulses.

Although the embodiment of FIG. 1 has shown the case where the crank angle sensor is provided in a distributor, the invention is applicable to the case where the crank angle sensor is directly connected to a crankshaft.

The reference numeral 2a designates a suction pipe pressure sensor. Any one of the output of the sensor 2a and the output of the air-flow meter 2 is used for the feedback control of the fuel supply quantity and the ignition timing.

The control unit 15 has the construction as shown in FIG. 2. In the drawing, the reference numeral 151 designates an A/D (analog-to-digital) converter which receives the output S1 of the air-flow meter 2 or the output S1a of the suction pipe pressure sensor 2a, the output S2 of the water temperature sensor 6, the output S4 of the exhaust sensor 9, and the output S6 of the combustion pressure sensor 13.

The reference numeral 152 designates and input interface which receives the output S3 of the crank angle sensor 7.

The reference numeral 153 designates a CPU which operates together with an ROM 154 and an RAM 155 to process the aforementioned input signal in accordance with a predetermined program.

The reference numeral 156 designates an output interface which receives the output of the CPU 153 and produces its output signals S5 and S6. The output S5 is a pulse signal for actuating the fuel injection valve 10. The fuel supply quantity can be controlled by the pulse width of the pulse signal.

The output S7 is an ignition timing signal which is amplified by a power unit 16. The ignition coil 17 is operated by the output S8 of the power unit 16.

The output S9 of the ignition coil 17 is distributed as an output S10, by the distributor 18, into the ignition plugs 11 respectively provided in the cylinders.

In the following, the operation is described. The basic method for controlling the fuel injection and the ignition timing based on the output of the air-flow meter 2 or the suction pipe pressure sensor 2a in the apparatus of FIG. 1 is well known, and the detailed description thereof will be omitted. The operation related to the present invention will be therefore described in detail.

Referring to FIG. 3, the relation between the combustion pressure P_c and the crank angle θ_c is shown. In FIG. 3, the output S6 of the combustion pressure sensor 13 takes a maximum value in the vicinity of a crank angle upper dead point (TDC). Let the maximum value be P_max.

Mean effective pressure P_i (cylinder internal pressure) is calculated by integrating the combustion pressure P_c over one cycle as follows. ##EQU2##

In the equation (1), V_s is the piston displacement represented by the equation: ##EQU3## Further, V is the cylinder volume and represented by the following equation (2): ##EQU4## in which l is the control length, r is the piston stroke and θ_c is the crank angle.

Accordingly, the following equation (3) is obtained from the equation (2). ##EQU5##

Accordingly, the mean effective pressure P_i can be calculated by substituting the equation (3) into the equation (1).

The mean effective pressure P_i thus obtained is well known as a parameter for directly detecting the power output of the engine.

Other parameters A and B can be calculated from the mean effective pressure P_i, the suction air quantity Q_a of the engine obtained based on the output S1 of the air-flow meter 2 or the suction pipe pressure P_b obtained based on the output S1a of the suction pipe pressure sensor 2a, and the engine speed N obtained based on the crank angle. These parameters A and B are also useful as parameters for evaluating combustion energy or efficiency from the quantity (Q_a /N or P_b) of suction air per stroke, of the engine.

A=P.sub.i /(Q.sub.a /N)                                    (4)

B=P.sub.i /P.sub.b                                         (5)

Typical relations between these evaluation parameters (P_max, P_i, A, B), air-fuel ratio and ignition timing are as shown in FIGS. 4 and 5.

As shown in FIG. 4, P_max and P_i have maximum values. It is apparent from FIG. 4 that the maximum output power can be obtained by controlling the air-fuel ratio to maximize these parameters.

Further, the evaluation parameters A and B are parameters for expressing combustion energy which can be drawn out from the quantity of suction air per stroke. It is known that optimum efficiency can be obtained by controlling the air-fuel ratio to maximize the parameters A and B.

As shown in FIG. 5, P_max increases as the ignition timing θ_ig is advanced, but the mean effective pressure P_i and the evaluation parameters A and B have maximum values.

In the engine having such performance, the maximum power and optimum efficiency can be obtained by controlling the ignition timing to maximize the mean effective pressure P_i and the evaluation parameters A and B.

The aforementioned controlling operation will be described more in detail with reference to the flow charts of FIGS. 6(a) and 6(b). Referring now to FIG. 6(a), there is shown a flow chart for detecting combustion pressure. In the step 101, the output θ_c of the crank angle sensor is read out. The output of the crank angle sensor may be produced by counting pulses generated for every predetermined degree (for example, 1° ) of crank angle or may be produced in the form of a code corresponding to the angle.

Then, in the step 102, the output P_c of the combustion pressure sensor 13 is read out. The reading of P_c is carried out for every predetermined degree (for example, 1° ) of crank angle.

Then, in the step 103, a judgment is made as to whether P_c is larger than P'_max or not. Because P'_max is cleared up in an initial stage of one cycle of combustion, the first read value of P_c is larger than P'_max. Accordingly, in the step 104, P_c is kept at P'_max.

Then, in the step 105, the mean effective pressure P'_i is calculated by the aforementioned equation. Then, in the step 106, a judgment by the value of crank angle signal θ_c is made as to whether one cycle of combustion is terminated or not. When not terminated, the step is returned to the step 101.

As described above, P'_max is successively updated to a larger value by the step 104 when P_c increases. When P_c decreases, the procedure of the step 104 is omitted so that the maximum value of P_c in one combustion cycle can be kept at P'_max.

At the point of time one cycle is terminated, the step is shifted from the step 106 to the step 107. In the step 107, P'_max is stored in P_max. Then, in the step 108 p'_i is stored in P_i. Then, in the step 109, P'_max and P'_i are cleared up. Thereafter, the aforementioned procedure from the step 101 is repeated for a new cycle.

The aforementioned values of P_max and P_i are used in the following fuel control and ignition timing.

FIG. 6(b) is a flow chart for controlling the fuel injection quantity to maximize the mean effective pressure P_i obtained by the procedure of FIG. 6(a). Though not shown, the initial values P_i(0) and P_i(1) of the mean effective pressure P_i are set to be zero.

In FIG. 6(b), the step 201 is provided for reading mean effective pressure P_i held in a (n-1)th combustion cycle, that is to say, the reading P_i(n-1). Similarly, the step 202 is provided for reading mean effective pressure P_i held in a (n)th combustion cycle, that is to say, for reading P_i(n).

Then, in the step 203, the sizes of P_i(n) and P_i(n-1) are discriminated. Because P_i(1) is equal to P_i(0) in the initial stage, the step is shifted to the step 204. In the drawing, T_n represents a pulse width by which the fuel injection valve was operated at the last time. In the initial stage, T_n is set to be a pulse width T₀. This pulse width T₀ corresponds to the reference air-fuel ratio (A/F)₀ in FIG. 4. A pulse width T₁ for the next combustion cycle is obtained by subtracting ΔT from the pulse width T₀.

Then, in the step 206, the fuel injection valve is operated by the pulse width T₁. Because the pulse width T₁ is less than the pulse width T₀ by ΔT, the air-fuel ratio is shifted to a lean side in FIG. 4 so that the mean effective pressure P_i(2) produced by this injection becomes larger than P_i(1).

This mean effective pressure P_i(2) is read out in the step 207. In the step 208, the mean effective pressure P_i(0) is replaced by P_i(1). In the step 209, the mean effective pressure P_i(1) is replaced by P_i(2). Further, in the step 210, the pulse width T₀ is replaced by T₁. Thereafter, the step is returned to the step 201.

As described above, the pulse width T_n+1 is reduced whenever Δ is subtracted by the step 204. Consequently T_n+1 approaches the pulse width T_opt corresponding to the optimum air-fuel ratio (A/F)_opt as shown in FIG. 4.

When T_n+1 is further reduced to be smaller than the pulse width T_opt, the mean effective pressure P_i is reduced reversely.

Because the relation P_i(n) <P_i(n-1) is established in the step 203, the step is shifted to the step 205. In the step 205, the pulse width T_n+1 is reversely set to be larger than the last value T_n by ΔT.

When the aforementioned operation is repeated, the pulse width T_n+1 is converged in the vicinity Of T_opt so that the mean effective pressure P_i is adjusted to be in the vicinity of its maximum value. The subtrahend ΔT is established to be as small as possible. The reason is in that the pulse width T_n+1 changes widely in the vicinity of T_opt as the subtrahend ΔT increases, to thereby make stable driving in a value sufficiently near T_opt impossible.

FIG. 6(b) is a drawing simplified for the purpose of explaining the principle of operation. For this reason, the following operation error may occur.

Assuming now that the pulse width T_n is between T₀ and T_opt, then the pulse width T_n can be converged into T_opt by the subtraction shown in the step 204. However, if the addition in the step 205 is mistaken for the subtraction in the step 204, the mean effective pressure P_i decreases and, accordingly, the addition in the step 205 is carried out based on the judgment of the step 203 in the next cycle. Consequently, the pulse width will diverge toward the pulse width T₀. The aforementioned problem can be solved logically as shown in FIG. 6(c).

FIG. 6(c) shows the point of improvement. Other portions not shown in FIG. 6(c) are the same as those in FIG. 6(b). In FIG. 6(c), the step 303 is provided for setting the flip-flop I to be 0 when the subtraction is carried out in the step 204. Similarly, the step 304 is provided for setting the flip-flop I to be 1 when the addition is carried out in the step 205. After the procedure of the

step

304 or 303, the step is shifted to the step 206.

In the next cycle, the value of the flip-flop I is judged by the

steps

301 and 302 after the judgment of the step 203. If the flip-flop I has been set to be 0 when the step is shifted from the step 203 to the step 203, the mean effective pressure P_i has increased as the result of the subtraction. Accordingly, in this case, the subtraction in the step 204 is carried out again to approach the pulse width T_n+1 to T_opt.

If the flip-flop I has been set to be 1, the mean effective pressure P_i has increased as the result of the last addition. Accordingly, a decision that the pulse width is on the right side of T_opt (that is, T_n+1 <T_opt) is made. Accordingly, the step is shifted to the step 205, so that the addition in the step 205 is carried out to approach the pulse width T_n+1 to T_opt. The operation in the step 302 is the same as described above.

It is apparent from the above description that the flip-flop I is provided for making a judgment as to whether the pulse width T_n+1 is on the right side of T_opt or not to thereby prevent the pulse width from diverging in the reverse direction as stated preliminarily.

Of course, in the initial stage, the flip-flop I must be set to be 0 as well as the pulse width is set to be T₀.

The method for controlling the mean effective pressure P_i by controlling the fuel supply quantity has been described with reference to FIGS. 6(a) through 6(c). The method for controlling the mean effective pressure P_i by the ignition timing θ_ig will be understood easily when the pulse width T shown in the drawings is replaced by the ignition timing θ_ig. Accordingly, the detailed description thereof will be omitted.

Similarly, the control method for maximizing the maximum combustion pressure P_max and the evaluation parameters A=P_i /(Q_a /N), B=P_i /P_b will be understood easily when the mean effective pressure P_i shown in the drawings is replaced by these parameters. Accordingly, the detailed description thereof will be omitted.

In the following, another embodiment of the present invention in which the aforementioned control method is practically applied is described. FIG. 7 shows an example of the maximum value control according to the present invention in the apparatus for performing feedback control so as to make the air-fuel ratio be a predetermined value by use of the exhaust sensor.

In the drawing, the step 401 is provided for making a judgment as to whether the air-fuel ratio feedback control based on the exhaust sensor can be executed or not. The judgment is made from the operation condition of the engine, the breakdown of the exhaust sensor and the like.

In the case where this control is executed, the step is shifted to the step 402. In the step 402, the output of the exhaust sensor 9 is read out. Then, in the step 403, the fuel supply quantity feedback control is carried out to adjust the output of the exhaust sensor to a predetermined value. The controlling procedure is known commonly and the detailed description thereof will be omitted.

Then, in the step 404, the ignition timing θ_ig is controlled to maximize at least one of the evaluation parameters P_max, P_i, A and B. The control procedure is carried out by the maximum value control as explained above with reference to FIGS. 6(a) through 6(c).

Then, the step is shifted to the step 405, when a decision that the air-fuel ratio feedback control is not executed is made in the step 401. In the step 405 the fuel supply quantity Q_f is controlled to maximize at least one of the evaluation parameters P_max, P_i, A and B. This control operation has been described with reference to FIGS. 6(a) through 6(c).

Then, the ignition timing θ_ig is controlled by the procedure of the step 404. The flow chart of FIG. 7 is constructed so that the maximum value control based on the fuel supply quantity Q_f is not executed while the air-fuel ratio feedback control is executed. In short the component concentration of an exhaust gas is kept in a predetermined level or less, so that the air fuel ratio is controlled preferentially.

FIG. 8 shows a method for averaging the evaluation parameters used in the aforementioned control. In the drawing, the step 501 is provided for reading the parameter X_i (which is the value of P_max, P_i, A or B in an (i)th cycle of combustion and corresponds to the output of the

step

107 or 108 in FIG. 6(a)). In the step 502, the parameter X_i is integrated successively.

The step 503 is provided for making a judgment as to whether the number of integrating operations has reached n (cycles) or not. If the number has not reached n, the step is shifted to the step 504 in which the average value X is obtained by dividing the integrated value by n. The control in FIGS. 6(b), 6(c) and 7 is carried out by the average value X. The averaging is made in consideration of the case where the combustion pressure P_c or the evaluation parameter P_max, P_i, A or B changes slightly to thereby interfere with the maximum value control though the engine is operated in the same fuel supply quantity Q_f and in the same ignition timing θ_ig.

Considering the fact that learning speed becomes slower because of the averaging, it is necessary to determine n within a range allowable for the control. After the averaging, the integrated value is cleared up in the step 505.

Although FIG. 8 shows a simple arithmetic averaging method, other known methods such as a weighted averaging method and a moving averaging method can be used.

In the maximum value control as explained above, it is desired that the controllable range related to the ignition timing control and the fuel supply quantity control is limited. The reason is that lagging ignition timing causes an accidental fire or injury due to overheating of an exhaust gas and, on the contrary, leading ignition timing causes lowering of output power or injury due to abnormal combustion. In the case where the fuel supply quantity is too much or in the case where the fuel supply quantity is too little, the same trouble occurs.

The limitation can be realized by controlling the ignition timing θ_ig and the fuel injection pulse width by upper and lower limits when they are beyond the upper and lower limits. The logic is simple and description with reference to the drawing will be omitted.

As described above with reference to FIG. 6(b), the addend or subtrahend ΔT (or Δθ_ig in the case of ignition timing) used for every cycle must be established to be as small as possible.

However, the fact that the addend or subtrahend is small means that the pulse width (ignition timing) is converged into an optimum value slowly. Accordingly, the fact is unsuitable for the control of the engine in which the operating condition changes continuously.

To solve such a problem, the operating condition of the engine is separated into zones by the operation parameter. The maximum value control by means of the injection pulse width T_n or the ignition timing θ_ig(n) is carried out for every zone. The results of the control, that is, T_n and θ_ig(n) are stored in memories provided corresponding to the zones. The memories may be capable of storing the results continuously after the power supply is cut.

In this case, the correction of the control parameters T_n and θ_ig(n) can be started from the vicinity of the respective optimum values when the engine is restarted or when the engine operating condition is shifted from one to another. Accordingly, the rate of convergence can be improved so that preferable control can be made.

To realize this control, the RAM 155 in FIG. 2 can be provided as a nonvolatile memory or the power supply for the RAM 155 can be backed up by a battery to keep the contents of the RAM 155.

FIG. 9 is a view showing an example of the zone separation of the operation condition and the assignment of the memories. In the drawing, the abscissa expresses the engine speed N which is separated into N₁, N₂ and N₃. The ordinate Y expresses parameter showing the load of the engine. The suction air quantity Q_a, the value Q_a /N obtained by dividing the suction air quantity Q_a by the engine speed N, suction pipe pressure P_b and the like are used as the parameter. The ordinate Y is similarly separated into Y₁, Y₂, Y₃ and Y₄.

Zone separation is carried out by N and Y so that memories M_T l,_m and Mθl,_m are assigned corresponding to the respective zones. In FIG. 9, M_T represents a memory for keeping the control parameter T_n , Mθ represents a memory for keeping the control parameter θ_ig(n), and l and m represent separation numbers in the abscissa and the ordinate, respectively.

In the case where the operation condition is in these zones, the maximum value control is carried out so that the control parameters are temporarily written in the memories M_T and Mθ and kept therein. Although FIG. 9 shows the case where the operation condition is separated into zones by two-dimensional parameters of the engine speed N and the parameter Y showing the load of the engine, it is a matter of course that the operation condition can be separated into zones by a single parameter N or Y.

The logic of control in FIG. 9 is simple and the description thereof with reference to the drawing will be omitted.

The control parameters stored in the memories M_T and Mθ can be converted into proper values when the engine is stably operated in a corresponding zone.

In the case where acceleration and deceleration are repeated on the engine, however, the maximum value control may be carried out corresponding to the transient state of combustion so that aberrant values may be stored in the memories.

To solve such a problem, a filter as shown in FIG. 10 can be used. In FIG. 10, the step 601 is provided for reading the pulse width T_n (the value of the step 210 in FIG. 6(b)) as one of the maximum value control parameters. Then, in the step 602, the last value T_o (old) which has been stored in the memory M_T is read. In the step 603, the following arithmetic operation is carried out based on T_n and T_o (old).

T.sub.o (new)=(1-K).T.sub.o (old)+KT.sub.n

In the arithmetic operation, K satisfies the relation 0<K≦1.

The meaning of this arithmetic operation is that a value T_o (new) to be newly kept in the memory is produced so that K times the currently obtained result T_n is reflected in the memory. The value of K is determined by even balance between the suitable convergence speed of the value to be kept in the memory and the suppression of aberrant correction value in the transient state.

Then, in the step 604, the pulse width T_o (new) is written in the memory M_T. Thereafter, the step is returned to the step 601. The value T_o stored in the memory M_T is used as an initial value of pulse width T_n when the maximum value control of FIG. 6(b) starts.

In FIG. 10, the steps 601 to 604 may be circulated in synchronism with the maximum value control of FIG. 6(b) or may be circulated in a more lagging cycle.

Although FIG. 10 shows the case where the pulse width T_n is used as one of the control parameters, it is a matter of course that the ignition timing θ_ig(n) can be stored in the memory M in the same manner as described above.

The execution of the aforementioned maximum value control had better stop when the operation of the combustion pressure sensor 13 is abnormal. Accordingly, a range of output value obtained from the combustion pressure sensor 13 which is in a normal state had better be determined in advance so that a flag for inhibiting the maximum value control can be set when a value beyond the range is obtained from the combustion pressure sensor 13. In short, the flag is read when the maximum value control starts, so that the control is inhibited when the flag is in a set state. This logic is simple and the description thereof with reference to the drawing will be omitted.

The judgment as to whether the output of the combustion pressure sensor 13 is normal or not can be made by using at least one of the combustion pressure P_c directly obtained from the combustion pressure sensor 13, the maximum value P_max of the combustion pressure P_c and the mean effective pressure P_i.

FIG. 11 is a diagram showing the engine control apparatus according to another embodiment of the present invention.

In this embodiment, a throttle valve 3 for adjusting the inflow of air is provided in an air-intake passage 22 of an engine 21. An air-flow sensor 2 for detecting the inflow of air is provided in an upstream side of the air-intake passage 22. An injector 26 for injecting fuel toward a combustion chamber 5 is connected to the air-intake passage 22. An air-fuel ratio sensor (O₂ sensor) 28 for detecting the oxygen concentration of exhaust gas to generate a detection signal which changes widely by reference to a theoretical air-fuel ratio is provided in an exhaust passage 8 of the engine 21. A water temperature sensor 6 is provided in a tank 29 filled with water for cooling the engine. An ignition plug 11 for igniting a mixed gas in the combustion chamber 5 is provided in a cylinder head 31 of the engine 21. A cylinder internal pressure sensor 13 for detecting pressure in the combustion chamber 5 is further provided in the cylinder head 31. The ignition plug 11 is electrically connected to an ignition coil 17 through a distributor 18 which is provided with a rotation sensor 16 for detecting the rotation of the engine.

The injector 26 and the ignition coil 17 are controlled by a control unit 15. The control unit 15 receives various detection signals from the air-flow sensor 2, the cylinder internal pressure sensor 13, the rotation sensor 16 and the air-fuel ratio sensor 28. As shown in FIG. 12, the control unit 15 is composed of a CPU 100, an A/D converter 101 for converting various analog input signals into digital signals and for supplying those digital signals to the CPU 100, an input ROM 103 for storing in advance the procedure for controlling the CPU 100, an RAM 104 for use in the arithmetic process of the CPU 100, and

output circuits

105 and 106 for supplying control signals to the injector 6 and the ignition coil 17 respectively.

FIG. 13 is a graph of combustion pressure (P₀) versus Crank angle. FIG. 14 is a characteristic graph showing the condition in which mean effective pressure (P_i) obtained from the relationship between combustion pressure P₀ and crank angle is changed corresponding to the change of ignition timing. In the present invention, a control operation is carried out so that the crank angle having the maximum value of P₁ can be used as target ignition timing. In particular, in a high load range, the air-fuel ratio feedback control is carried out so that the maximum value of P₁ becomes highest.

The control unit 15 calculates the quantity (Q_a) of suction air (Q_a) and the engine speed (N_e) and judges the load on the basis of the value Q_a /N_e. When the load is not larger than a predetermined value, that is to say, when the load is in the range of P in FIG. 15, ordinary fuel injection control is carried out and, at the same time, the ignition timing feedback control based on the internal pressure of the cylinder is carried out to obtain the maximum value of mean effective pressure (P_i) in a stationary state. On the contrary, when the load is larger than the predetermined value, that is to say, when the load is in the range of E in FIG. 15, the ignition timing feedback control based on the internal pressure of the cylinder is carried out to obtain the maximum value of P₁ in a stationary state and, at the same time, fuel cylinder is carried out to maximize P₁.

In the following, the control operation of this embodiment is described more in detail with reference to the flow chart of FIG. 16. In the drawing, symbols S₁ to S₁₃ designate various steps respectively.

At the start, the quantity of suction air (Q_a) is read in the step S₁. In this step, analog signals from the air-flow sensor 2 are converted into digital values by the A/D converter 101 so that, if necessary, the digital values are averaged as the quantity of suction air (Q_a).

Then, the engine speed (N_e) is read in the step S₂. In this step, N_e is obtained by reading and measuring the interval of the pulse signals of the rotation sensor 16.

Then, the quantity of air per engine revolution (Q_a /N_e) is calculated corresponding to the quantity of load of the engine in the step S₃.

Then, in the step S₄, the output signal of the cylinder internal pressure sensor 13 is read whenever a crank angle signal is generated from the rotation sensor 16. In the step S₅, mean effective pressure (P_i) is calculated based on the values of the output signals of the cylinder internal pressure sensor 13.

Then, in the step S₆, the judgment of load is carried out by judging whether the value of Q_a /N_e is larger than a predetermined value α₁ or not.

If Q_a /N_e is not larger than α₁, the judgment proves that the load is in the partial load range so that the step is shifted from S₆ to S₇. In the step S₇, the air-fuel ratio feedback control (O₂ feedback control) is carried out based on the output signal of the air-fuel ratio sensor 28.

Then, in the step S₈, a judgment is carried out as to whether the O₂ feedback control is in operation or not. If the answer is "YES", the step is shifted to S₉. In the step S₉, a judgment is carried out as to whether the load is in a stationary state or not. The judgment as to whether the O₂ feedback control is in operation or not is based on the judgment as to whether various conditions, such as water temperature conditions and air-fuel ratio sensor (O₂ sensor) activating conditions, are satisfied or not. In general, the conditions of the judgment are used in ordinary fuel injection control. On the other hand, the judgment of stationary state is based on the judgment as to whether the absolute value of the deviation of Q_a /N_e per unit time is less than a predetermined value or not (Q_a /N_e may be replaced by Q_a). In other words, the judgment of stationary state is based on the judgment as to whether road conditions and the quantity of displacement of the accelerator are constant or not.

If the judgment proves that the driving condition is in a stationary state in the step S₉, ignition timing is controlled to maximize P_i. The ignition timing control is carried out within a variable range between a lower limit A₁ and an upper limit B₁.

If the judgment proves that the O₂ feedback control is not in operation in the step S₈ or if the judgment proves that the driving condition is not in a stationary state in the step S₉, the step is returned to the initial step S₁.

Then, if the relation Q_a /N_e >α₁ is satisfied in the step S₆, that is to say, if the load is in a high load range, the step is shifted to the step S₁₁ to judgment whether the driving condition is in a stationary state or not. The judgment in the step S₁₁ is the same as the judgment in the step S₉.

Then, if the judgment proves that the driving condition is in a stationary state in the step S₁₁, the step is shifted to S₁₂. In the step S₁₂, ignition timing is controlled to maximize P_i. In this case, the ignition timing control is carried out within a variable range between a lower limit A₂ and an upper limit B₂. Although the air-fuel ratio feedback control is carried out in the partial load range, the change of air-fuel ratio is large in the high load range. Accordingly, the variable range of ignition timing in the high load range is less than the variable range of ignition timing in the partial load range. For example, the variable range of ignition timing in the high load range is from -5° _CA (A₂) to +5° _CA (B₂) and the variable range of ignition timing in the partial load range is from -10° _CA (A₁) to +10° _CA (B₁).

Then, the step is shifted to S₁₃ to control the quantity of fuel to maximize P_i. The fuel control is carried out within a variable range between a lower limit A₃ and an upper limit B₃.

Although the aforementioned embodiment has shown the case where the feedback control is carried out based on mean effective pressure calculated, as a value corresponding to the torque of the engine, from detection values of internal pressure of the cylinder, the invention is applicable to the case where the feedback control of the ignition timing and the air-fuel ratio may be carried out by using as a standard parameter the crank angle at which the internal pressure of the cylinder takes a peak value, to obtain highest torque.

Although the aforementioned embodiment has shown the case where the air-fuel ratio is controlled by controlling the quantity of fuel injection, the means for controlling air-fuel ratio is not limited to the fuel injection controlling method.

The present invention is realized in the form of other embodiments.

As described above, according to the first invention, ignition control is carried out based on the fuel supply quantity Q_f or the ignition timing θ_i to maximize at least one of the maximum pressure P_max, the mean effective pressure P_i and the evaluation parameters A and B for every combustion cycle. Further, according to the second invention, feedback control of the fuel supply quantity Q_f is carried out to make the air-fuel ratio be a predetermined value and, at the same time, the ignition timing θ_i is corrected to maximize at least one of the maximum pressure P_max, the mean effective pressure P_i and the evaluation parameters A and B. Further, according to the third invention, feedback control of the fuel supply quantity Q_f is carried out to make the air-fuel ratio be a predetermined value, while the feedback control is stopped in a predetermined range of the engine load and, at the same time, the fuel supply quantity Q_f or the ignition timing θ_i is corrected to maximize at least one of the maximum pressure P_max the mean effective pressure P_i and the evaluation parameters A and B. Accordingly, maximum output power and maximum efficiency can be obtained in spite of scatter in performance of engines.

In addition, power and efficiency can be improved while interference between the air-fuel ratio feedback control based on the exhaust sensor and the maximum value control based on the combustion parameter is suppressed and, at the same time, the component concentration of exhaust gas is kept in a predetermined level or less.

Further, because the present invention is configured as described above, the air-fuel ratio feedback control as well as the ignition timing feedback control can be made in accordance with the internal pressure of the cylinder even in a high load range where the air-fuel ratio feedback control could not be made in the prior art. Consequently, the best in the torque of the engine can be brought out.

Claims

What is claimed is:

1. An internal combustion engine control apparatus comprising:

an air-flow meter for measuring a suction air quantity Qa of an engine;

a suction pipe pressure sensor for detecting suction pipe pressure P_b of said engine;

a crank angle sensor for detecting the revolution angle θ of said engine;

at least one cylinder internal pressure sensor for detecting combustion chamber pressure P_c of said engine; and

a control unit which comprises;

means for obtaining a fuel supply quantity Q_f and an ignition timing θi from an engine speed N and one of said suction air quantity Qa and said suction pipe pressure P_b ;

means for obtaining at least one of maximum pressure value P_max, a mean effective pressure P_i, a first evaluation parameter A=P_i (Qa/N) and a second evaluation parameter B=P_i /P_b, said maximum pressure P_max and said means effective pressure P_i being calculated from said combustion chamber pressure and said revolution angle θ_c for every combustion cycle, said first evaluation parameter A being calculated from said suction air quantity Q_a, said engine speed N and said mean effective pressure P_i, said second evaluation parameter B being calculated from said suction pipe pressure P_b and said mean effective pressure P_i ; and

means for correcting at least one of said fuel supply quantity θ_f and said ignition timing θ_i to maximize said at least one of said maximum pressure value P_max, said mean effective pressure P_i, and said first and second evaluation parameters A and B;

means for controlling one of a fuel supply quantity and an ignition timing on the basis of a corrected value obtaining from said correcting means; and

an exhaust sensor for detecting the component concentration of a combustion gas,

wherein said control unit further comprises means for obtaining an air-fuel ratio based on the component concentration of the combustion gas detected by said exhaust sensor, and means for performing a feedback control of said fuel supply quantity θ_f to set said air-fuel ratio to a predetermined value, said correcting means corrects said ignition timing θ_i to maximize said at least one of said maximum pressure value P_max, said mean effective pressure P_i, and said first and second evaluation parameters A and B; and

wherein in a predetermined load-operation range of said engine, said feedback control and the correlation of said ignition timing θ_i are executed whereas out of said load-operation range of said engine, said feedback control is stopped and said ignition timing θ_i is corrected to maximize at least one of said maximum pressure P_max, said mean effective pressure P_i and said first and second evaluation parameters A and B.

2. An engine control apparatus comprising:

air-fuel ratio control means for controlling an air-fuel ratio of an engine;

ignition timing control means for controlling the ignition timing of said engine;

air-fuel ratio detection means for detecting the air-fuel ratio of said engine;

load detection means for detecting the load of said engine;

cylinder internal pressure detection means for detecting the internal pressure of at least one cylinder of said engine;

first feedback control signal generation means responsive to the output of said cylinder internal pressure detection means for outputting a first feedback control signal to said ignition timing control means to substantially maximize the output torque of said engine on the basis of the cylinder internal pressure detected by said cylinder internal pressure detection means;

load judgment means responsive to the output of said load detection means for judging whether the load of said engine is in a low or partial load range or in a high load range.

air-fuel ratio feedback control signal generation means for outputting an air-fuel ratio feedback control signal to said air-fuel ratio control means to converge the air-fuel ratio detected by said air-fuel ratio detection means to a theoretical value when said load judgment means judges that the load of said engine is in said low or partial load range; and

second feedback control signal generation means responsive to the output of said cylinder internal pressure detection means for outputting a second feedback control signal to said air-fuel ratio control means to substantially maximize the torque of said engine when said load judgment means judges that the load of said engine is in said high load range.